A conventional speaker system includes, for example, an L channel speaker unit, an R channel speaker unit and a center speaker unit (for example, see Patent Document 1). Each of the above three speaker units is arranged in the center of positions ahead of the driver's seat and passenger seat of a vehicle. The L channel speaker unit is directed toward a direction in which the directivity axis of the L channel speaker unit is rotated counterclockwise in the horizontal direction with respect to the traveling direction of the vehicle and in which the directivity axis is inclined at a predetermined angle to the vertical direction with respect to the traveling direction of the vehicle. The R channel speaker unit is directed toward a direction in which the directivity axis of the R channel speaker unit is rotated clockwise in the horizontal direction with respect the traveling direction of the vehicle and in which the directivity axis is inclined at a predetermined angle in the vertical direction with respect to the traveling direction of the vehicle. The center speaker unit outputs an −L-R signal obtained by adding an −L signal which is a reverse phase signal of an L channel signal and an −R signal which is a reverse phase signal of the R channel signal.    Patent Document 1: Japanese Patent Application Laid-Open No. 2004-289341